DE102007021330A1 - Fuel injector for an internal combustion engine with common rail injection system - Google Patents

Abstract

A fuel injector (10) comprises an injector housing (12), a stroke-controlled valve element (28) which cooperates on the one hand with a housing-side sealing seat (33) and on the other hand limits a hydraulic control chamber (48), and a fluid path (40) from a high-pressure port (42) leads to the sealing seat (33). It is proposed that the fluid path (40) extends over a closing piston (58) which is coupled to the valve element (28), that the fluid path (40) comprises a flow restrictor (68) over the closing piston (58) and the region (40a) of the fluid path (40) lying between the closing piston (58) and the high-pressure connection (42) comprises a relief valve (70).

Description

State of the art

The The invention relates to a fuel injector for an internal combustion engine with common rail injection system according to the preamble of the claim 1.

from Market ago are known internal combustion engines with a common rail, to which a plurality of fuel injectors are connected, the inject the fuel directly into their assigned combustion chambers. The known fuel injectors have over a stroke-controlled valve element, which with a housing-side Seating works together and a lift off from this seal seat one Fuel outlet from fuel outlet channels in the Combustion chamber allows. One in a hydraulic control room prevailing control pressure acts on the valve element in his Closed position. The control pressure can be opened the valve element can be lowered. The advantage of such stroke-controlled Fuel injectors is that the injection pressure to the load and Speed of the internal combustion engine can be adjusted.

To improve the emission values, a high injection pressure is advantageous. In order nevertheless to keep the leakage amount low, a valve element is used, which is completely surrounded by high fuel pressure, ie without a so-called "low-pressure stage" manages. To improve the closing behavior and the stability of such a fuel injector, especially in the metering small injection quantities is not pre-published in the DE 10 2006 036 447.3 suggested a slight throttling of the fuel in the fluid path from the high pressure port to the sealing seat, whereby an additional hydraulic closing force is generated. In addition, there is shown to increase the pressure surface acting in the closing direction by using an additional annular closing piston.

Disclosure of the invention

task the present invention is to provide a fuel injector which, with high injection pressure and low leakage, provides a good closing and opening behavior.

These Task is according to the invention with the features of claim 1. Advantageous developments of Invention are specified in subclaims. About that In addition, find essential features of the invention also in the following description and the figures, wherein the features alone or in different combinations for the invention may be essential without being affected each explicitly indicated.

By the use of a closing piston, with the valve element is coupled, the pressure acting in the closing direction pressure surface specifically enlarged, reducing the closing behavior even with a valve element which has no low pressure stage and instead completely of fuel at high pressure is surrounded, improved by increasing the closing force becomes. In the same direction, the inventively provided acts Flow restrictor, which by means of the flowing Fuel also an additional hydraulic closing force generated.

The According to the invention provided relief valve limits the pressure difference across the flow restrictor away, to a maximum value. In that regard, the relief valve can also be referred to as a pressure relief valve. This can be a Too high, acting in the closing direction force when opening of the valve element can be avoided. According to the invention was namely, recognized that by the closing piston and the flow restrictor when opening the valve element Fuel from between high-pressure port and closing piston lying room must be displaced, the one against the opening movement acting pressure difference at the flow restrictor entails. Through the relief valve, the pressure in this between high pressure port and closing piston lying Range is limited to a maximum value, which makes it too high closing force when opening the valve element is avoided. This will improve the performance of the fuel injector stabilized. In addition, the pressure loss, the for generating a sufficiently large closing force is required, reduced, which in turn the efficiency of the invention Fuel injector improved. A simple realization possibility is that the relief valve fluidly parallel to Flow restrictor is arranged.

A first embodiment of the fuel injector according to the invention is characterized in that the relief valve to the between closing piston and sealing seat lying fluid path opens. This improves the efficiency of the fuel injector, as from the between Closing piston and high pressure connection lying fluid path downstream Fuel is used for the injection.

A compact and easy to manufacture construction of the invention Fuel injector provides that the closing piston annular and coaxial with the valve element.

In this case, the relief valve may be arranged in the closing piston. The injector can thus remain unchanged, so that the inventions According to provided relief valve does not affect the manufacturing cost of the injector.

Of the Closing piston may further integrally with the injector or be formed on this. This eliminates the handling an additional separate part during assembly of the Fuel injector, which simplifies the production.

Especially but it is also advantageous if the closing piston a Valve element of the relief valve forms. The closing piston is in this respect also a pressure relief or relief piston, leaving an additional component to limit the pressure in the lying between high pressure port and closing piston Area of the fluid path or to limit the pressure difference between this area and between closing piston and sealing seat lying area is not required.

In Further development is proposed that the closing piston by a spring, which is supported on the valve element against a sealing portion is acted on the valve element. Thus, will the closing force acting on the closing piston on the Transfer spring to the valve element. In the episode can the closing force can be kept almost constant, so that Pressure oscillations only slightly on the closing force impact. This leads to an improvement of the injection tolerances, The amount of fuel is therefore with higher precision injected.

Also to reduce manufacturing costs contributes when the flow restrictor is arranged in the closing piston. An additional Processing of the injector housing for the realization of the flow restrictor is not necessary then.

Especially simply the flow restrictor can also be realized be that between closing piston and an adjacent one Section a gap is realized. This can be a Annular gap or act around a longitudinal groove through which the Cleft is realized locally.

advantageously, the closing piston in the injector is fluid-tight guided. The associated with the closing piston Sealing seat thus lies on the valve element, so that by the closing piston at least in idle state no additional closing force is exerted on the valve element.

In Continuing this is proposed that between closing piston and valve element a radial clearance is present. This will be a consuming to produce double guide of the valve element avoided.

Brief description of the drawings

following Embodiments of the present invention are disclosed With reference to the accompanying drawings explained in more detail. In the drawing show:

1 a partial and schematic section through a first embodiment of a fuel injector;

2 a representation similar 1 a second embodiment; and

3 a representation similar 1 a third embodiment.

embodiments the invention

A fuel injector carries in 1 Overall, the reference number 10 , It is used in an internal combustion engine (not shown) with a common-rail injection system for direct injection of the fuel into a combustion chamber directly assigned to the fuel injector.

The fuel injector 10 includes a multi-part injector housing 12 which, in 1 from top to bottom, a control valve piece 14 , an end plate 16 , an elongated injector body 18 and a nozzle body 20 includes. At the in 1 lower end of the nozzle body 20 are multiple fuel outlet channels 22 present, through which the fuel in the operation of the fuel injector 10 is injected into the associated combustion chamber.

In the injector body 18 is a through hole 24 and in the nozzle body 20 a to this subsequent stepped bore 26 available. In these is a long-drawn valve element 28 taken, which is a control rod 30 and, to the fuel exit channels 22 adjacent, a nozzle needle 32 includes. This in 1 lower end of the nozzle needle 32 works with a housing-side sealing seat 33 together. The lower end of the control rod 30 is about leadership sections 34 in the nozzle body 20 guided. Between the guide sections 34 are flattened areas 36 available. In 1 immediately below the guide sections 34 or the flattened areas 36 is at the nozzle needle 32 a conical and in the opening direction acting pressure surface 37 available. On the in

1 upper end of the control rod 30 is a sealing sleeve 38 placed. This is supported by its upper edge on the end plate 16 from.

Between the valve element 28 and the injector housing 12 is an annulus 40 educated. The This is with a high pressure connection 42 connected, in turn, to a common rail 44 connected. An in 1 upper end surface of the control rod 30 forms a hydraulic control surface 46 , This limits together with the sealing sleeve 38 and the end plate 16 a hydraulic control room 48 , Via an inlet throttle 50 this communicates with the annulus 40 , About a drain throttle 52 communicates the hydraulic control room 48 with an electromagnetic switching valve 54 , which in open position the hydraulic control room 48 with a low pressure connection 56 combines. In one embodiment, not shown, instead of the electromagnetic switching valve 54 also a piezoelectric valve are used.

To tension the valve element 28 between the sealing sleeve 38 and the guide sections 34 To avoid, can on the valve element 28 Provided areas with reduced bending stiffness (in 1 not shown). Alternatively, the valve member may comprise a control rod and a nozzle needle which are coupled together or otherwise mechanically interconnected via a hydraulic coupler without substantially transmitting bending moments from one member to the other. It is further understood that in an embodiment not shown, the valve element may be in one piece, and / or that the valve element may be significantly shorter than in the 1 illustrated embodiment.

The fuel injector 10 has an annular and the valve element 28 coaxial closing piston 58 , with its radially outer lateral surface (without reference numeral) in the stepped bore 26 in the nozzle body 20 is guided fluid-tight. Between the radially inner lateral surface (without reference numeral) of the closing piston 58 and the control rod 30 of the valve element 28 is a gap 60 present, for a radial clearance between closing piston 58 and valve element 28 provides. At the control rod 30 is, in 1 below the closing piston 58 , a support ring 62 rigidly attached. This extends radially outward slightly further than the gap 60 so that the closing piston 58 can rest on him. For this purpose, the closing piston 58 from a transmission sleeve 64 subjected to the same with radial play on the control rod 30 deferred and between closing piston 58 and sealing sleeve 38 is arranged. Between transmission sleeve 64 and sealing sleeve 38 is a compression spring 66 braced. Through this, on the one hand, the sealing sleeve 38 against the end plate 16 and on the other hand, the closing piston 58 against the support ring 62 applied.

In the closing piston 58 is a flow restrictor 68 arranged, which is designed as a throttle bore and one between the high pressure port 42 and closing piston 58 located area 40a of the annulus 40 with a between closing piston 58 and seal seat 33 lying area 40b of the annulus 40 combines. In an alternative, not shown embodiment, the flow restrictor 68 simply through an annular gap between closing piston 58 and injector housing 12 or a groove in the radially outer surface of the closing piston 58 educated.

Furthermore, in the closing piston 58 a relief valve formed by a spring-loaded check valve 70 integrated, which to the between closing piston 58 and seal seat 33 located area 40b of the annulus 40 opens and in this open state the area 40a and 40b of the annulus 40 connects with each other. As a valve element comprises the relief valve 70 a valve ball 72 coming from a valve spring 74 against one on the closing piston 58 trained sealing section 76 is charged. One recognizes that the fuel injector 10 includes a fluid path from the high pressure port 42 over the area 40a of the annulus 40 , by means of the flow restrictor 68 and optionally also by means of the (open) relief valve 70 over the closing piston 58 away to the area 40b of the annulus 40 So over the flattened areas 36 to the sealing seat 33 leads. The relief valve 70 is thus fluidly parallel to the flow restrictor 68 arranged.

The fuel injector 10 works as follows: At rest, with closed switching valve 54 , prevails throughout the annulus 40 the at the high pressure connection 42 ruling high fuel pressure. This is via the inlet throttle 50 also in the hydraulic control room 48 transferred into it. The corresponding force resulting from the hydraulic control surface 46 acts on the valve element 28 in the closing direction of the valve element 28 against the seal seat 33 , The fluid path described above thus ends at the sealing seat 33 , Fuel can through the fuel outlet channels 22 do not leak. The relief valve 70 is closed.

If fuel is to be injected, the electromagnetic switching valve 54 open, eliminating fuel from the hydraulic control room 48 over the outlet throttle 52 to the low pressure connection 56 flows. This reduces the pressure in the hydraulic control room 48 and accordingly, the one on the hydraulic control surface decreases 46 acting and acting in the closing direction force results. Fall in the closing direction on the valve element 28 acting forces under the pressure surface 37 acting in the opening direction, the valve element moves 28 up. The high fuel pressure in the range 40b now also works on the lower conical tip 72 the nozzle needle 32 , which additionally creates forces in the opening direction the valve element 28 Act.

With the opening movement of the valve element 28 shifts due to the entrainment through the support ring 62 also the closing piston 58 up, reducing the volume of the area 40a of the annulus 40 is reduced. The flow through the flow restrictor 38 over the closing piston 58 away adjusting pressure difference between the areas 40a and 40b is thereby reinforced, which is an additional acting in the closing direction hydraulic force on the closing piston 58 generated, extending over the support ring 62 also on the valve element 28 effect. This could, without countermeasures, to slow down the opening movement of the valve element 28 and this leads to stability problems. These will be at the in 1 illustrated fuel injector 10 however, by the function of the relief valve 70 avoided: By this is namely a maximum possible pressure difference between the areas 40a and 40b of the annulus 40 set. Exceeds the pressure difference between these two spaces 40a and 40b the opening pressure difference of the relief valve 70 , this opens, reducing the pressure in the room 40a in the room 40b is relieved.

When the fuel injection is terminated, the electromagnetic switching valve becomes 54 closed, eliminating the escape of fuel from the hydraulic control room 48 to the low pressure connection 56 is ended. About the inlet throttle 50 fuel flows into the hydraulic control room 48 after, so that there the pressure rises again approximately to that level, which in the annulus 40a or at the high-pressure connection 42 prevails. Due to the flow restrictor 68 the pressure is in the range 40b of the annulus 40 slightly lower than in the area 40a and thus also slightly lower than in the hydraulic control room 48 , Despite equal area between on the one hand the hydraulic control surface 46 and on the other hand the printing surface 37 and the conical tip 72 now prevail in the closing direction on the valve element 28 acting forces - also because of the closing piston 58 in addition, a force acting in the closing direction acts - so that they are again in the direction of the sealing seat 33 emotional. Approaches the nozzle needle 32 the seal seat 33 , the pressure on the conical tip decreases 72 due to throttling effects, whereby the opening direction on the valve element 28 decrease forces acting again and the closing process is accelerated. Is the nozzle needle 32 again at the sealing seat 33 On, no fuel can escape from the fuel exit channels 22 exit, and it ends the fuel flow from the area 40a in the area 40b , It now returns to a state in which throughout the annulus 40 and in the hydraulic control room 48 approximately the same hydraulic pressure prevails.

An alternative embodiment of a fuel injector 10 is in 2 shown. Here, as in the following, such elements and regions which have equivalent functions to elements and regions which have already been explained in connection with a preceding figure bear the same reference numerals.

The in 2 illustrated fuel injector 10 is different from that of 1 in that the closing piston 58 not in the area of the nozzle body 20 but in the area of the injector body 18 , near the sealing sleeve 38 is arranged. A transmission sleeve is therefore not necessary. In addition, the closing piston 58 integral with the control rod 30 formed a gap between the control rod 30 and closing piston 58 does not exist.

Another alternative embodiment shows 3 : In this, the valve element 72 the relief valve 70 through the closing piston 58 self-educated. The sealing section 76 with which the closing piston 58 co-operates by a collar on the control rod 30 realized. Against this is the closing piston 58 by a spring 74 impinged on a support ring 62 supported.

Exceeds the pressure difference between the areas 40a and 40b of the annulus 40 a desired value, in particular during the opening operation of the valve element 28 , lifts the closing piston 58 from the ring collar 76 which causes fuel in addition to the flow restrictor 68 from the area 40a in the area 40b can escape, which is the pressure in the annulus 40a limited. At the same time, that is on the closing piston 58 acting and in the closing direction of the valve element 28 acting hydraulic force on the spring 74 and the support ring 62 on the control rod 30 and the nozzle needle 32 transfer.

The in the embodiments in the 1 and 2 comparatively rigid coupling between the closing piston 58 and the valve element 28 takes place at the in 3 embodiment shown so on the spring 74 , The feather 74 it acts steaming, so that pressure fluctuations especially in the area 40a of the annulus 40 only reduced to the valve element 28 impact. As a result, the precision of the metering of the injected fuel quantity is improved. Again, it is understood that in an embodiment, not shown, the ring collar 76 , Closing piston 58 or valve element 72 and valve spring 74 existing arrangement also higher up in the injector body 18 can be arranged. It is also conceivable all embodiments described above, the flow restrictor 68 through the opening gap between the valve element 72 the relief valve 70 and the associated sealing portion 76 to realize.

QUOTES INCLUDE IN THE DESCRIPTION

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Cited patent literature

• - DE 102006036447 [0003]

Claims (11)

Fuel injector ( 10 ) for an internal combustion engine with common rail injection system, with an injector housing ( 12 ), a stroke-controlled valve element ( 28 ), which on the one hand with a housing-side sealing seat ( 33 ) and on the other hand a hydraulic control room ( 48 ) and with a fluid path ( 40 ) connected by a high-pressure connection ( 42 ) to the sealing seat ( 33 ), characterized in that the fluid path ( 40 ) via a closing piston ( 58 ), which is connected to the valve element ( 28 ), that the fluid path ( 40 ) over the closing piston ( 58 ) a flow restrictor ( 68 ), and that between closing piston ( 58 ) and high pressure connection ( 42 ) lying area ( 40a ) of the fluid path ( 40 ) a relief valve ( 70 ). Fuel injector ( 10 ) according to claim 1, characterized in that the relief valve ( 70 ) to the between closing piston ( 58 ) and sealing seat ( 33 ) fluid path ( 40b ) opens. Fuel injector ( 10 ) according to one of claims 1 or 2, characterized in that the closing piston ( 58 ) annular and coaxial with the valve element ( 28 ). Fuel injector ( 10 ) according to one of the preceding claims, characterized in that the relief valve ( 70 ) in the closing piston ( 58 ) is arranged. Fuel injector ( 10 ) according to one of the preceding claims, characterized in that the closing piston ( 58 ) with the valve element ( 28 ) is integral. Fuel injector ( 10 ) according to one of claims 1 or 2, characterized in that the closing piston ( 58 ) a valve element ( 72 ) of the relief valve ( 70 ). Fuel injector ( 10 ) according to claim 6, characterized in that the closing piston of a spring ( 74 ) located on the valve element ( 28 ), against a sealing portion ( 76 ) on the valve element ( 28 ) is applied. Fuel injector ( 10 ) according to one of the preceding claims, characterized in that the flow restrictor ( 68 ) in the closing piston ( 58 ) is arranged. Fuel injector according to one of the preceding Claims, characterized in that the flow restrictor a gap between closing piston and an adjacent Section includes. Fuel injector ( 10 ) according to one of the preceding claims, characterized in that the closing piston ( 58 ) in the injector housing ( 12 ) is guided. Fuel injector ( 10 ) according to claim 10, characterized in that between closing piston ( 58 ) and valve element ( 28 ) a radial play ( 60 ) is available.